Characterization of fulvic acid fractions obtained by sequential extractions with pH buffers, water, and ethanol from paddy soils

Increasing industrial development and rapid urbanization affects adversely the paddy regions of China in terms of environmental pollution. Soil organic matter is one of the major components, which influence the contaminants mobility in soils. Fulvic acid is one of the major fractions of the soil organic matter of the paddy soils. It is imperative to separate fulvic acids (FA) to different fractions based on their chemical properties to reduce their heterogeneity and to cognize their environmental behavior. Five FA fractions from two paddy soils were first obtained by eluting FA through XAD-8 resin with sequential eluents (pH 4.8, pH 7.0, and pH 11 buffering solutions, water, and ethanol), and were then characterized by elemental analysis, Fourier-transform infrared (FT-IR) spectroscopy, liquid 1H nuclear magnetic resonance (1H NMR) spectroscopy, and cross-polarization magic-angle spinning 13C nuclear magnetic resonance (CP-MAS 13C NMR) spectroscopy. The results are consistent between the methods used, suggesting that the later eluted fractions (eluted with water or ethanol) in the sequential elution contained lower carboxylic C, and higher alkyl C than the earlier ones. We hope that such fractionation of humic matters would be useful in detail understanding of the interaction between natural organic matter and contaminants.